Split mechanical face seal with resilient pivoting member

ABSTRACT

A split mechanical face seal that provides fluid sealing between a housing and a rotating shaft includes first and second seal rings each having at least two seal ring segments and a radially extending seal surface. The seal ring surfaces of the seal rings are opposed to one another. One of the seal rings is connected to the rotating shaft to rotate therewith, while the other seal ring is connected to the housing. The split seal also includes a mechanism for introducing a fluid to the seal surfaces of the first and second seal rings. The seal further is provided with a system for maintaining co-planar alignment of the seal faces.

BACKGROUND OF THE INVENTION

The present invention relates generally to seals for providing fluidsealing between a housing and a rotating shaft. More particularly, theinvention relates to face seals in which a fluid is introduced betweenportions of the seal faces of the seal.

Conventional mechanical seals are employed in a wide variety ofmechanical apparatuses to provide a pressure-tight and fluid-tight sealbetween a rotating shaft and a stationary housing. The seal is usuallypositioned about the rotating shaft, which is mounted in and protrudesfrom the stationary housing. The seal is typically bolted to the housingat the shaft exit, thus preventing loss of pressurized process fluidfrom the housing. Conventional split mechanical seals include face typemechanical seals, which include a pair of annular sealing rings that areconcentrically disposed about the shaft, and axially spaced from eachother. The sealing rings each have sealing faces that are biased intophysical contact with each other. Usually, one seal ring remainsstationary, while the other ring contacts the shaft and rotatestherewith. The mechanical seal prevents leakage of the pressurizedprocess fluid to the external environment by biasing the seal ringsealing faces into physical contact with each other. As a result of therepeated physical contact between the faces, abrasion of the seal facesoccurs and the seals typically exhibit undesirable wear characteristicsand leakage.

The poor wear characteristics of these conventional mechanical faceseals necessitate the frequent monitoring and replacement of the sealcomponents, particularly the seal rings. Replacement and repair ofdamaged seals have been facilitated by seal designs where a portion ofthe component parts of the mechanical seals are segmented or split.Installation of split or partially split seal components can beperformed without necessitating the complete breakdown of the mechanicalapparatus and without having to pass the annular seal over an end of theshaft. However, even in split seal designs, significant time is requiredto replace the seal components, resulting in frequent long periods ofdown time for the mechanical apparatuses associated with the seal.

The prior art attempted to overcome the above difficulties by employingnon-contact mechanical seals that utilize a fluid interposed between theseal ring faces to reduce frictional wear. Conventional mechanicalnon-contact face seals typically employ spiral type-grooves formed inthe hard face of the seal rings to develop a hydrodynamic lifting forcethat separates the seal faces. The resultant gap allows fluid to bedisposed within the gap to prevent abrasion of the seal faces. Thesetypes of seals are limited in application because the seals are designedto operate in a unidirectional manner. If the seals are driven in theopposite direction, the seal rings typically do not separate but arepulled or sucked toward each other, thereby increasing wear andultimately destroying the seals. Other conventional designs employspecially designed spiral grooves that can operate in both directions(bi-directional grooves). These grooves, however, are typically lessefficient in separating the seal faces.

Even in mechanical non-contact seal designs a certain amount of sealface abrasion occurs, especially during start-up or during periods inwhich the shaft is rotating at relatively low speeds. Such abrasioncausing wear of the seal components requires the eventual replacement ofthe seal components.

Few, if any, split-seal designs have been proposed for non-contactingseals. Difficulties have occurred in developing such a seal design dueto the increased number of sealing surfaces in a split seal design andthe presence of the fluid between the seal faces. The additional sealsurfaces between each of the split segments of the seal components, andespecially between the seal ring segments, make it difficult to maintaina fluid tight seal throughout the split seal. In addition, the fluidinterposed between the seal faces can exert separation forces on thesplit seal components which can cause separation of the split componentsand further fluid leakage. For these reasons, there is a need in the artfor a split, non-contact mechanical seal design that can provide afluid-tight seal, while concomitantly providing the advantage ofconventional split-seal designs.

As the above described and other prior art seals have proved less thanoptimal, an object of the present invention is to provide an improvedsplit mechanical seal in which a fluid can be introduced between theseal faces while maintaining a relatively fluid-tight seal.

Another object of the invention is to provide a split mechanical sealoperable under a wide range of operating conditions for a wide range ofservices.

Still another object of the present invention is to provide a splitmechanical seal that is relatively easy to assemble or and todisassemble.

Yet another object of the invention is to provide a split mechanicalseal that employs fluid at the seal faces to reduce wear whileconcomitantly preventing or minimizing leakage at the other faces,without compromising seal performance or integrity.

Other general and more specific objects of this invention will in partbe obvious and will in part be evident from the drawings and thedescription which follow.

SUMMARY OF THE INVENTION

These and other objects are attained by the split mechanical face sealof the present invention in which each of the components of the seal canbe split and a barrier fluid can be introduced to the seal faces of thestationary and rotary seal rings. The split mechanical seal of thepresent invention provides the advantages of a non-contacting sealdesign, e.g., reduced wear on the seal faces, as well as the advantagesof split mechanical seal design, e.g. ease of installation andmaintenance, while concomitantly preventing process fluid leakage acrossthe seal surfaces. Additionally, the split mechanical seal of thepresent invention provides for adjustment of the degree of contactbetween portions of the seal faces and the flexibility and advantage ofbeing suitable for gas or liquid barrier fluids applications, as well asfor multiple environments.

The invention provides a split mechanical face seal that provides fluidsealing between a housing and a rotating shaft and includes first andsecond seal rings each having at least two seal ring segments and aradially extending seal face. The seal ring faces of the seal rings areopposed to one another. One of the seal rings is connected to androtates with the rotating shaft, while the other seal ring is connectedto the housing. The split mechanical seal includes means for introducinga fluid to the seal faces of the first and second seal rings. The sealalso includes means for maintaining co-planar alignment of the sealfaces.

Fluid pressure variations at the seal faces can result in distortion ofthe seal faces. Pressure related distortion of the seal faces can causeconing--deflection of one of the seal faces in a manner that causes theseal faces to depart from a co-planar relationship. Coning can result inloss of the fluid seal between the housing and the rotating shaft. Themeans for maintain co-planar alignment of the seal faces provided in theseal of the present invention controls coning of the seal faces.

The means for maintaining co-planar alignment of the seal faces caninclude a resilient member positioned about the second seal ring topermit pivoting of the second seal ring about the split resilientmember. By enabling pivoting of the second seal ring about the resilientmember, co-planar alignment of the first and second seal faces can bemaintained.

The split seal can optionally include a split gland assembly having atleast two gland segments that sealingly engage an outer surface of thefirst seal ring and connect the first seal ring to the housing. Thesplit support member can also include at least one split resilientmember, such as a split O-ring, interposed between the split glandassembly and the outer surface of the first seal ring for resilientlysupporting the first seal ring in the radial direction.

The split seal can also optionally include a split holder assemblyhaving at least two holder segments for connecting the second seal ringto the rotating shaft. At least one split resilient member, such as asplit O-ring, can be interposed between the split holder assembly andthe outer surface of the second seal ring. The split resilient membercan resiliently support the second seal ring in the radial direction andthe axial direction.

The means for introducing a barrier fluid can be a groove formed in thefirst seal face. The groove can be continuous about the first seal faceand can be positioned to form two concentric seal faces on the firstseal face thereby providing a dual seal. A continuous, circumferentialgroove can also be positioned on the first seal face to form lands onboth sides of the circumferential groove. The barrier fluid can be a gasor a liquid or a combination thereof. In conjunction with other factors,such as the pressure of the barrier fluid, the groove can be dimensionedsuch that the barrier fluid within the groove provides a primarilyhydrostatic force on the first and second seal faces to cause separationof at least a portion of the first seal face from at least a portion ofthe second seal face.

The means for introducing a barrier fluid to the first and second sealfaces can include a fluid conduit formed through the first seal ring.The fluid conduit can have an opening at the first seal face and canextend substantially axially through the first seal ring to open at theouter surface of the first seal ring. A second fluid conduit can beformed in the split support member. The second fluid conduit can bepositioned proximate to and in fluid communication with the fluidconduit formed in the first seal ring.

The split seal can optionally include a system for introducing a closingfluid to a rear surface of the first seal ring. The closing fluid exertsa closing force on the first seal ring that biases the first and secondsealing faces towards one another into a sealing relationship. Thesystem for introducing a closing fluid can be a fluid conduit formed inthe split support member. The fluid conduit can have an openingproximate the rear surface of the first seal ring to facilitate theintroduction of the closing fluid to the rear surface.

The split seal can also include a system for fluidly retaining the sealring segments of the first seal ring in a sealing relationship in anegative pressure condition. The system for fluidly retaining the sealring segments of the first seal ring in a sealing relationship caninclude a fluid conduit formed in the first seal ring for supplyingbarrier fluid to the outer surface of the first seal ring. The fluidconduit can have an opening in fluid communication with the means forintroducing barrier fluid to the first and second seal faces.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bemore fully understood by reference to the following detailed descriptionin conjunction with the attached drawings in which like referencenumerals refer to like elements through the diferent views. The drawingsillustrate principals of the invention and, although not to scale, showrelative dimensions.

FIG. 1 is a fragmentary view in cross-section of a split mechanicalseal, illustrating the structure for introducing a fluid to the sealfaces according to the teachings of the present invention;

FIG. 2 is a perspective view of one-half of the gland-assembly of thesplit mechanical seal of in FIG. 1 according to the teachings of thepresent invention;

FIG. 3 is a perspective view of one-half of the assembled splitmechanical seal of FIG. 1 according to the teachings the presentinvention;

FIG. 4 is a perspective view of one-half of the rotary seal ring of thesplit mechanical seal of FIG. 1 according to the teachings of thepresent invention;

FIG. 5 is a perspective view of one-half of the rotary seal ring holderassembly of the split mechanical seal of FIG. 1 according to theteachings of the present invention;

FIG. 6 is perspective view of one-half of the stationary seal ring ofthe split mechanical seal of FIG. 1 according to the teachings of thepresent invention;

FIG. 6A is a perspective view of one-half of the stationary seal ring ofthe split mechanical seal of FIG. 1, illustrating an alternativearrangement of the fluid bores formed in the stationary seal ring;

FIG. 7A is a perspective view of a gland or holder assembly screwaccording to the teachings of the present invention;

FIG. 7B is a side elevational view of the screw of FIG. 7A;

FIG. 8 is a top fragmentary view of the gland assembly of the split sealof FIG. 1 according to the teachings of the present invention;

FIG. 9 is a side elevational view of a face of a rotary seal ring holdersegment of the split mechanical seal of FIG. 1 according to theteachings of the present invention;

FIG. 10 is a side elevational view of a face of a rotary seal ringsegment of the split mechanical seal of FIG. 1 according to theteachings of the present invention;

FIG. 11 is a side elevational view of a stationary seal ring segment ofthe split seal of FIG. 1 according to the teachings of the presentinvention;

FIG. 12 a side elevational view of a stationary seal ring segment and arotary seal ring segment of the split mechanical seal of FIG. 1illustrating the separate force that develop within the seal ring grooveaccording to the teachings of the present invention;

FIG. 13 is a fragmentary side elevational view of the seal ring faces ofthe split seal shown in FIG. 12 further illustrating the forces withinthe groove according to the present invention;

FIG. 14 is a sectional view of an elastomeric member according to thepresent invention;

FIG. 15 is a fragmentary view in cross-section of the split mechanicalseal shown in FIG. 1 according to the present invention;

FIG. 15A is a fragmentary view in cross-section of the holder assemblyand the rotary seal ring of the split mechanical seal shown in FIG. 1according to the present invention;

FIG. 16 is an exploded unassembled view of the seal components of FIG. 3according to the present invention;

FIGS. 17A-C are side elevational views in cross-section of thestationary seal ring segment and the rotary seal ring segment of thesplit mechanical seal of FIG. 1 illustrating pivoting of the rotary sealring; and

FIG. 18 is a broken, side elevational view of the gland assembly of thesplit mechanical seal of FIG. 1 illustrating the fastener aperturesformed therein according to the present invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

U.S. patent application Ser. No.: 08/992,751, filed on Dec. 17, 1997 andentitled SPLIT MECHANICAL FACE SEAL WITH NEGATIVE PRESSURE CONTROLSYSTEM and co-pending U.S. patent application Ser. No. 08/992,611 filedon Dec. 17, 1997 and entitled SPLIT MECHANICAL FACE SEAL WITH SEAL FACEFLUID INTRODUCING STRUCTURE, (Attorney Dovket No. CHT-279), all of whichare incorporated herein by reference. The mechanical seal 10 ispreferably concentrically disposed about a shaft 12 and is secured to anexternal wall of a housing 11, such as a pump or the like. The shaft 12extends along an axis 13, and is mounted, at least partially, in thehousing 11. The seal 10 is constructed to provide fluid sealing betweenhousing 11 and shaft 12. thereby preventing a process medium fromescaping the housing 11. Fluid sealing is achieved by a stationary sealring 14 and a rotary seal ring 16, each ring having a radially extendingarcuate seal face 20, 18 and a pair of segment sealing surfaces 22 and24, as shown in FIGS. 4, 6, and 16. The seal face 18 of seal ring 14 isbiased into a sealing relationship with the seal face 20 of seal ring16, as described in greater detail below. In addition, the segmentsealing surfaces 22, 24 of each seal ring are biased into sealingengagement with each other. Thus, these individual seal surfaces providea fluid seal operable under a wide range of operating conditions and ina wide range of services, as described in greater detail below.

The terms "process medium" and "process fluid" used herein generallyrefer to the medium or fluid being transferred through the housing 11.In pump applications, for example, the process medium is the fluid beingpumped through the pump housing.

The terms "axial" and "axially" used herein refer to a directiongenerally parallel to shaft axis 13. The terms "radial" and "radially"used herein refer to a direction generally perpendicular to shaft axis13.

The split mechanical seal 10 is preferably a split mechanicalnon-contacting-type face seal in which a barrier fluid is introducedbetween the seal faces 18, 20 of the first and second seal rings 14, 16,respectively. In a non-contacting-type face seal the barrier fluid actsto minimize, inhibit, or prevent contact between substantial radialportions of the seal face 18 and radial portions of the seal face 20,thereby reducing the frictional engagement and the resulting wear of theseal faces 18, 20. Accordingly, a non-contacting-type face seal includesseal designs in which there is total separation of the seal faces at alltimes, total separation of the seal faces under certain conditions,i.e., during periods of shaft rotation, and occasional or partialseparation of the seal faces. In contrast, a contacting-type face sealincludes seal designs in which partial or complete contact of the sealfaces is maintained. In both type of seals, the barrier fluid functionsas a heat transfer medium to transfer heat away from the seal faces toreduce the effects of thermal stress on the seal faces.

The barrier fluid used with the present seal can be a gas or a liquid ora combination of both. Typically, the area of the seal faces thatremains in frictional contact is greater in barrier liquid applicationsthan in barrier gas applications. Accordingly, the use of a barrier gascan result in less frictional wear on the seal faces 18, 20 relative tothe use of barrier liquid. A gas barrier fluid, however, is not suitablefor all applications due to the slight amount of leakage of the barriergas into the process medium that will occur. The use of barrier liquidin the seal can provide increased reduction of the effects of thermalstress due to the typically better heat transfer properties of a liquidcompared to a gas. One skilled in the art will appreciate that thechoice of one fluid medium over another is dependent on the type ofservice in which the seal is used. For example, in applications in whicha minimal amount of barrier gas leakage is acceptable, a barrier gas maybe preferred to reduce wear at the seal faces and to increase the lifeof the seal. In services in which the presence of a minimal amount ofbarrier gas within the process medium is undesirable, a liquid seal maybe preferable.

Accordingly, the seal of the present invention provides the flexibilityand the unique advantage of being suitable for both gas or liquid (orcombinations thereof) barrier fluid applications. In addition, many ofthe features of the mechanical seal of the present invention, asdescribed herein, are suitable for use in traditional mechanical (i.e.,contacting) face seal applications as well as non-contacting face sealapplications. As such, the seal of the present invention is not solelylimited to a non-contact-type seal arrangement (e.g., a gas seal), butenjoys the unique advantages of both conventional split mechanical sealsand conventional gas seals in a simple but elegant seal design.

With reference to FIGS. 1 through 3 and 16, the illustrated splitmechanical seal 10 includes, in addition to the stationary seal ring 14and the rotary seal ring 16, a seal gland assembly 30 and a rotary sealring holder assembly 100. The sedal gland assembly 30 includes a pair ofidentical gland segments or halves 34a and 34b, one of which is shown inFIG. 2. The gland segment 34a has, starting from the axial outermost end(the bottom of FIG. 2), an inner surface that includes an axiallyextending first surface 36 and an integrally formed and axiallyextending second surface 38 that is radially stepped from the firstsurface 36. The first surface 36 and the second surface 38 form incombination therewith a first annular connecting wall 40. An axiallyextending third surface 42 is radially stepped from the second surface38 and forms, in combination therewith, a second annular connection wall44. The third surface 42 is axially segmented into three sections 42a,42b, and 42c by elastomeric receiving channels 46 and 48, each of whichis radially stepped from the third surface 42. An axially extendingfourth surface 50 is radially stepped from the third surface 42 by athird annular connection wall 52. A sloped fifth surface 54 extendsradially inward and axially outwardly from the gland segment fourthsurface 50.

The gland assembly 30 has a housing gasket groove 56 formed along abottom 58 of the gland assembly 30. The groove 56 seats a flat, annularelastomeric gasket 60 that preferably has an axial dimension greaterthan the depth of the groove 56, thereby providing a pressure-tight andfluid-tight seal between the mechanical seal 10 and the housing 11. In apreferred embodiment, the housing gasket 60 is pre-cut into two arcuatesegments for mounting in each gland segment 34a, 34b. The housing gasketsegments are preferably mounted in the groove 56 and secured thereto byan adhesive. This arrangement helps to prevent leakage of the processmedium along the mating portions of the mechanical seal 10 and thehousing 11 when mounted together.

Each axially extending gland seal surface 62, 63 has formed therein agland gasket groove 64. The groove 64 has a main axial portion 66 whichextends from the gland second surface 38 to the gland gasket groove 56.Groove segments 68 and 70, transverse to the main groove segment 66,extend to the second surface 38 and the gland gasket groove 56,respectively, and groove segment 72, spaced radially inward from maingroove segment 66, extends along the second seal surface 38. A pair ofinternal transverse groove segments 74 and 76 extend transversely frommain groove segment 66 to third gland surface 42, and groove segment 78,spaced radially inward from main groove segment 66, extends parallel tothe third gland surface 42 to connect transverse groove segments 74 and76.

Referring to FIGS. 1 and 3. an elastomeric gland gasket 80,complementary in shape to gland groove 66, seats in the groove. Thegasket 80 extends beyond the split gland seal surfaces 62, 63 whenseated in groove 66, as best shown in FIGS. 3 and 8. The exposed portionof the gasket 80 is captured in a complementary groove formed on thesplit gland seal face of the other gland segment 34b. Capturing bothends of the gasket 80 between the gland seal surfaces 62, 63 preventsthe gasket 80 from extruding into the gap formed between the split glandseal surfaces when subject to pressures higher than a selected maximumpressure. This double-capturing features allows the gland segments towithstand greater pressures without developing pressure leaks, as wellas relaxing the mechanical tolerances of other components of the seal10. The gland gasket 80 can be formed from any suitable resilientmaterial, such as elastomeric rubber. Further, although the gasket 80preferably has the illustrated shape, those of ordinary skill willrecognize that the gasket 80 and its corresponding groove 66 can haveany suitable geometric configuration.

With reference to FIGS. 2 and 3. each of the gland seal surfaces 62 and63 has pair of fastener receiving apertures 84 formed therein. Theapertures 84 have a tapped smaller-diameter portion 86, and a concentricuntapped larger-diameter portion 88. Preferably, the untapped portion 88of the aperture 84 is disposed closest to the gland seal surfaces 62,63. An alignment pin 82 extends from gland seal surface 63 and isreceived in an alignment aperture 83 formed in the seal surface of theother gland segment. The alignment pin 82 serves to ensure a somewhatproper alignment of the gland seal surfaces 62, 63 of the gland sealsegments 34a and 34b when assembled.

The apertures 84 mount screws 90 having the configuration illustrated inFIGS. 7A and 7B. The screw 90 preferably has a main shaft 92 and ascrew-head portion 96. The screw shaft 92 has a threaded distal portion93 and an untapped proximal portion 94. The outer diameter of thethreaded portion 93 is greater than the outer diameter of the proximalportion 94. As illustrated in FIG. 18, each screw 90 fastens together apair of gland segments 34a and 34b. When the threaded distal portion 93of the screw 90 is screwed into the tapped portion 86 of the aperture84, the distal portion 93 is positively maintained in the aperture 84.As the screw 90 further travels through the aperture 84, the screwdistal end enters the untapped portion 88, or clearance gap of theaperture 84. In this orientation, the screw 90, although not snuglysecured, is still positively maintained (i.e., is not detachable) in theaperture 84. In a preferred embodiment, the diameter of thedistalthreaded portion 93 mates with the diameter of the tappedsmaller-diameter portion 86.

The illustrated configuration of the screw 90 and the aperture 84 of thepresent invention provide significant advantages. In particular, thescrew 90 can be mounted in the fastener-receiving aperture 84 fromeither side of the gland segments 34a, 34b prior to assembly, which isparticularly useful in limited access installations, and is positivelymaintained in the gland segment. Preventing the screw 90 from completelydetaching from the gland segment prevents accidental loss of the screw90 during assembly and disassembly, thus facilitating assembly of theseal while reducing installation time.

Each of the gland segments include two fastener recesses 98 toaccommodate bolts (not shown) to mount mechanical seal 10 of theinvention to the housing 11. Alternatively, bolt-tabs may be providedabout the periphery of the seal 10 to facilitate connection of the seal10 to the housing 11. Examples of suitable bolt tabs are shown in U.S.Pat. No. 5,209,496 and U.S. Pat. No. 5,571.268, both of which areassigned to the assignee hereof and are incorporated herein byreference.

As illustrated in FIGS. 1, 3, 5, and 9. a holder assembly 100 isdisposed in a chamber 102, shown in FIG. 2, formed in gland assembly 30and is spaced radially inward therefrom. It should be understood,however, that the holder assembly 100 need not be disposed within thegland assembly 30. The holder assembly 100 has a pair of identicalarcuate holder segments 104a and 104b, one of which is shown in FIG. 5.As shown in FIGS. 5 and 9, each holder segment includes an outer surface106 and an inner surface 108. The holder segment inner surface 108 has aradially inward sloping first surface 110 that terminates in an axiallyextending second surface 112. A pair of successive radially inwardlystepped surfaces form a third surface 114 and a fourth surface 115,respectively. The second surface 112 and the third surface 114 have aradially inward extending first wall 118 integrally formed therebetween,and the third surface 114 and the fourth surface 115 have a radiallyinward extending second wall 120 integrally formed therebetween. Afurther pair of successive radially inwardly stepped surfaces form afifth surface 116 and a sixth surface 119, respectively. The fourthsurface 115 and the fifth surface 116 have a radially inward extendingthird wall 121 integrally formed therebetween, and the fifth surface 116and the sixth surface 119 have a radially inward extending fourth wall117 integrally formed therebetween. The diameter of the sixth surface119 is preferably equal to or slightly greater than the diameter of theshaft 12, to which the holder assembly 100 is to be attached.

The holder segment outer surface 106 has a first axially extending outersurface 122 and a radially inward sloping second outer surface 124. In apreferred embodiment, the outer diameter of the holder segment firstouter surface 124 is less than the diameter of the gland segment fourthsurface 50. This clearance allows the holder assembly 100 to seat withinthe gland assembly 30 for unobstructed rotational movement therein. Theouter diameter of the second outer surface 124 is preferably less thanthe inner diameter of the gland segment fifth surface 54. and preferablygreater than the gland segment third surface 42.

The sixth face 119 of the holder segment 104a has formed thereon anannular channel 126 for mounting a split shaft gasket 128. When mountedin the channel 126, the gasket 128 sealingly mates with the shaft 12,providing a fluid-tight seal along the holder and shaft interface (seeFIG. 1). The second wall 120 preferably has formed therein a cylindricalalignment bore 130 for receiving one end of an alignment pin 132 (FIG.1). The other end of the alignment pin 132 is received in acorresponding bore 134 in the rotary seal ring 16. The protrusion 132operates as a mechanical rotary means by biasing the rotary seal ring 16into rotational movement, as described in greater detail below.

The illustrated holder segments 104a, 104b have a holder gasket groove140, having the configuration illustrated in FIG. 5, formed on eachsplit holder seal face 136, 138. A holder gasket 142, complementary inshape to the groove 140, seats in groove 140. The holder gasket 142,when seated in the groove 140, extends beyond the holder seal faces 136,138, as best shown in FIG. 3. The exposed portion of the gasket 142seats in a complementary groove formed in the opposite holder segmentseal face. This arrangement provides for a fluid-tight seal at pressureshigher than a selected value, as described above. The gasket can becomposed of any suitable deformable material, such as elastomericrubber.

Each of the holder segments 104a, 104b have a pair of fastener-receivingapertures 144 that mount screws 146 (FIG. 16). The holder apertures 144are similar to the fastener-receiving apertures 84 of the gland segments34a, 34b and likewise screws 146 are similar to screws 90.Advantageously, the screws 146 and apertures 144 operate in theaforementioned manner.

The holder assembly 100, the gland assembly 30, and the screws 90 and146 can be formed from any suitably rigid material, such as, forexample, stainless steel.

With reference to FIGS. 4 and 10, the rotary seal ring assembly 16includes a pair of arcuate rotary seal ring segments 150a and 150b, oneof which is shown in FIG. 4. The rotary seal ring segments have asubstantially smooth arcuate inner surface 152. The inner diameter ofthe inner surface 152 of the rotary seal segments is greater than thediameter of the shaft 12 to permit mounting thereon.

The rotary seal segments outer surface 154 has a series of axiallyextending outer surfaces each of which is stepped radially inward fromthe other. An axially extending second outer surface 158 is steppedradially inwardly from a first axial extending outer surface 156. Thefirst outer surface 156 and the second outer surface 158 form incombination therewith a first annular connecting wall 160 that extendsradially between the first and second outer surfaces. A third axialextending outer surface 162 is stepped radially inward from the secondouter surface 158 by a second annular connecting wall 164 that extendsradially between the second and third outer surfaces. A fourth axiallyextending outer surface 166 is stepped radially inward from the thirdouter surface 162. The third outer surface 162 and the fourth outersurface 166 form in combination a third annular connecting wall 168 thatextends radially between the third and fourth outer surfaces. A fourthannular connecting wall 169 extends radially from the fourth outersurface 166 to the inner surface 152.

The stepped outer surface 154 of the rotary seal segments arecomplementary to the stepped inner surface 108 of the holder segments104a, 104b to permit mounting of the rotary seal segments into theholder segments. The diameter of the rotary seal segment fourth outersurface 166 is less than the diameter of the holder segment fifthsurface 116. Likewise, the diameters of the rotary seal segment secondouter surface 158 and the third outer surface 162 are less than thediameters of the holder segment third surface 114 and fourth surface115, respectively.

Elastomeric members, such as split O-rings 170 and 172, can beoncentrically disposed about the rotary seal ring 16. In a preferredembodiment, the O-ring 170 seats along holder segment second surface 112and rotary seal segment second outer surface 158 and can selectivelyabut either first connecting wall 160 or holder segment first wall 118,as shown in FIGS. 1, 9, 10 and 15A. The O-ring 172 seats along theholder segment fourth surface 115 and third wall 121 and abuts rotaryseal segment fourth outer surface 166 and third connecting wall 168. TheO-rings 170 and 172 are sufficiently resilient to place each of therotary segment sealing surfaces 24 into sealing contact with thecorresponding seal ring segment, thereby forming a fluid-tight andpressure-tight seal. The O-rings 170 and 172 function to apply, incombination with the process fluid, a radially inward force thatresiliently biases the axial seal surfaces 24 of the rotor segmentstogether thereby preventing or minimizing leakage through the sealfaces. In addition, the O-ring 172 applies axial support to the rotaryseal ring 16 to inhibit axial motion of the rotary seal ring 16.

Fluid pressure variations between the seal faces 18 and 20, as well asat the outer and inner diameter surfaces of the seal faces, can resultin distortion of the seal faces 18 and 20a, b. This type of distortioncan cause coning of the seal faces. The term "coning" refers to thedeflection of one of the seal faces in a manner that causes the two sealfaces to depart from a co-planar relationship. Coning typically resultsin unwanted seal face contact at either the outer or the inner diameterof the seal rings.

To prevent coning, the O-ring 172 is positioned along the outer surface154 of the rotary seal ring segments 150a and 150b at a locationapproximately along axis 400 passing through the rotary seal ring 16, asillustrated in FIG. 17C. In this position, the O-ring 172 acts as aresilient pivoting member about which the rotary seal ring can pivot.The pivoting action of the O-ring 172 operates to maintain the sealfaces 18 and 20 in co-planar alignment.

FIG. 17A and 17B illustrates in exaggerated form the effects of coningon the rotary seal ring seal face 20 when the O ring 172 is positionedat a position other than along the axis 400. The specific location ofaxis 400, and thus O-ring 172, is dependent upon a number of factors,such as the magnitude of the fluid pressure forces on the rotary sealring and the specific dimensions of the seal ring. The location of axis400 for a particular seal ring configuration can be readily determinedby one skilled in the art using conventional finite element analysistechniques. In FIG. 17A, pressure distortions at the seal faces 18 and20a, b cause the inner diameter portion of the rotary seal face portion20a to deflect toward the stationary seal ring seal face 18 and theouter diameter portion of seal face portion 20b to deflect away fromseal face 18. In FIG. 17A, the O-ring 172 is positioned radially inwardfrom the axis 400. Conversely, in FIG. 17B, the O-ring 172 is positionedradially outward from the axis 400. Thus, pressure distortions at theseal faces 18 and 20a, b cause the outer diameter portion of seal faceportion 20b to deflect toward seal face 18 and the inner diameterportion of the seal face portion 20a to deflect away from the seal face18.

The pivoting action of the O-ring 172 provides for a resilient pivotingof the seal face 20 during full operation of the split mechanical seal10 in both non-contacting and contacting face seal modes, whileconcomitantly ensuring either consistent co-planar contact between theopposed seal faces or maintenance of a predetermined gap size betweenthese faces.

Those skilled in the art will recognize that the O-rings 170 and 172 arenot limited to the specific positions described herein. Alternatepositions are possible, including, but not limited to, seating thepivoting resilient member (O-ring 172) at a rear surface of the statorseal ring 14 to provide a similar seal face alignment function.

The illustrated seal face 20 of the rotary seal ring segments has acontinuous, arcuate circumferential groove 180 formed therein, as isbest shown in FIG. 4. In a preferred embodiment, the groove 180 isradially disposed between the inner surface 152 and the first outersurface 156 of the rotary seal ring 16. The groove 180 accordinglysplits the rotary seal ring seal face 20 into two concentric seal facesor land portions 20a and 20b. In this manner a dual seal is formedbetween the stationary seal ring 14 and the rotary seal ring 16.

With reference to FIGS. 1, 12 and 13, the groove 180 communicates withthe seal face 18 of the stator seal ring 14. A barrier fluid at aspecified regulated pressure, generaly greater than the processpressure, is introduced to the groove 180 through barrier fluid conduits228 formed in the stator seal ring 14, as is described in further detailbelow. The barrier fluid acts to provide a separation force to the sealfaces 18 and 20, as indicated by the arrows labeled F_(A) in FIGS. 12and 13. The separation force is a primarily hydrostatic force thatoperates to minimize, inhibit, or prevent contact between radialportions of the seal face 18 and radial portions of the seal faces 20aand 20b, thereby reducing the frictional engagement and the resultingwearing of the seal faces 18, 20a, 20b. The magnitude of the separationforce is dependent on a number of factors, such as, for example, thedimensions of the groove, e.g., axial depth and radial width, theconfiguration of the seal faces, the size of the conduit 228, as well asthe pressure of the barrier fluid. The choice of barrier fluid is also afactor when selecting the magnitude of the separation force and thedegree of seal face separation. In applications in which the barrierfluid is a gas, less seal face contact is desirable and, thus, a greaterdegree of seal face separation is preferred. In barrier liquidapplications, a smaller degree of seal face separation is required dueto the increased heat transfer properties of a liquid compared to a gas.

A significant advantage of the split mechanical seal 10 of the presentinvention is that it allows for the introduction of a cooling or barrierfluid to the seal faces 18, 20 of the seal rings 14, 16. A furtheradvantage of the seal of the present invention is that the seal canoperate with either a gas or liquid by adjusting the degree of seal facecontact, as well as the size of the gap formed between the seal faces 18and 20. When a liquid is used, the seal can revert to a conventionalbalance arrangement to operate as a conventional contacting mechanicalface seal. Conversely, when a gas is used, the seal operates as anon-contacting mechanical face seal in which the seal faces arepartially or completely separated. When operating in the non-contactmode, the degree of seal face contact, i.e., the magnitude of the gapbetween the seal faces, can be controlled and balanced by a closingfluid system, as described below. operating in combination with theO-ring 172, as well as, by adjusting the barrier fluid pressure at thegroove 180. Thus, the groove 180 and the axial bores 228, in combinationwith these other features, allow convenient operation of the splitmechanical seal in both non-contacting and contacting modes ofoperation, without regard to promoting leakage through the seal surfacesof the seal ring segments.

The barrier fluid within the groove 180 exerts a radially outward forceF_(Ro) and a radially inward force F_(Ri) on the rotary seal ring 16, asillustrated in FIGS. 12 and 13. Because the surface area at the outerwall 184 is greater than the surface area at the inner wall 186 of thegroove 180, these forces result in a net radially outward force F_(RO)on the rotary seal ring 16. The groove 180 is dimensioned such that theradially outward force F_(RO) created by the barrier fluid within thegroove does not generally exceed, and is indeed several orders ofmagnitude less than, the radially inward force F_(RI) on the rotary sealring 16 from the O-rings 170, 172 and from the process medium, asdescribed in detail below. Thus, the radially outward force F_(RO) dueto the barrier fluid does not separate or "blow apart" the rotary sealring segments 150a, 150b of the rotary seal ring 16.

An exemplary seal was constructed having a groove 180 dimensioned tohave an axial depth of 0.068 inches and a radial width of approximately0.25 inches. In this example, the groove was positioned approximately0.375 inches from the inner surface 152 of the rotary seal ring 16. Thisresulted in the radial width of the two rotary seal ring surfaces 20aand 20b being approximately 0.185 inches.

The seal of the present invention is not limited to the described andillustrated groove configurations, but can include other groove designs,such as, for example, a series of spiral grooves radially disposedbetween the inner surface 152 and the outer surface 156 of the rotaryseal ring 16. The spiral grooves accordingly split the rotary seal ringface 20 into the concentric seal faces 20a and 20b to form a dual seal.The spiral grooves can be uni-directional or bi-directional grooves.Barrier fluid within the grooves provides a primarily hydrodynamicseparation force between the seal faces 18 and 20a, 20b. Examples ofsuitable spiral groove designs are described in U.S. Pat. Nos.4,889,348, 5,143,384 and 5,529,315, all of which are incorporated hereinby reference.

With reference to FIGS. 1, 4, 10, 12 and 15, a plurality of axial bores183 extend through the rotary seal ring segments from the groove 180 tothe second annular connecting wall 164. The bores are preferably evenlyspaced apart along the circumference of the seal ring 16. Those ofordinary skill will recognize that any number and manner of spacing canbe utilized.

Barrier fluid can be introduced to outer surface 154 of the rotary sealring segments through the axial bores 183. As best illustrated in FIG.15, the O-rings 170 and 172, the outer surface 154 of the rotary sealring segments, and the inner surface 108 of the holder segments form, incombination therewith, a fluid-tight, pressure-tight annular chamber185. Barrier fluid introduced to the chamber 185 through the bore 228,the groove 180, and the axial bore 183 exerts a radially inward fluidforce F_(rr) on the outer surface 154 of the rotary seal ring segments(FIG. 15A). The radially inward fluid force F_(rr) acts in combinationwith the radial inward force provided by O-rings 170 and 172 and theprocess medium to place each of the rotary segment sealing surfaces 24into sealing contact with another segment, thereby maintaining afluid-tight and pressure-tight seal.

The radially inward fluid force F_(rr) can be varied or adjusted bycontrolling and/or regulating the pressure of the barrier fluid in thechamber 185. In this manner, the radially inward force on the rotaryseal ring segments can be adjusted to compensate for changes inoperating conditions within the seal. For example, a negative pressurecondition, in which the pressure of the fluid at the outer surface 154of the rotary seal ring segments drops below the pressure of the fluidat the inner surface 152 of the rotary seal ring segments, can result inseparation of the rotary seal ring segments, as is described in moredetail below. A negative pressure condition can also occur if the fluidpressure at the outer surface 154 drops below the pressure of thebarrier fluid introduced between the seal faces 18 and 20a, b. Thephrase "negative pressure condition" is defined herein to mean anycondition in which the pressure of the fluid at the outer surfaces ofthe seal rings and holder assembly is less than the pressure of thefluid at the inner surfaces of the seal rings and holder assembly or thepressure of the fluid introduced to the seal faces. In such a condition,the radially inward force F_(rr) can be increased to inhibit separationof the seal ring segments and thereby maintain the seal between the sealring segment surfaces 24.

In addition to the radially inward fluid force, the barrier fluid withinchamber 185 exerts an axial fluid force F_(ra) on the rotary sealsegments (FIG. 15A). Components of the axial fluid force F_(ra) aid inmaintaining O-rings 170 and 172 in their seated positions, as well asurge the seal faces of the rings toward each other. Axial fluid forcecomponent F_(ra1) biases O-ring 170 into sealing engagement with theouter surface 154 of the rotary seal ring segments and inner surface 108of the holder segments. The axial fluid force component F_(ra1) isopposed by an axial component of the process fluid face F_(pa) on theopposite side of O-ring 170. The O-ring 170 is free to move betweensurface 160 of the rotary seal ring 16 and surface 118 of the holderassembly 100, depending on which fluid pressure force is greater. Thisfreedom of movement is provided to facilitate pivoting of the rotaryseal ring about O-ring 172. The axial fluid force component F_(ra2)biases O-ring 172 into sealing engagement with the outer surface 154 ofthe rotary seal ring segments and inner surface 108 of the holdersegments.

A significant advantage of the negative pressure control feature of theillustrated seal is that it allows for a single mechanical seal tooperate in multiple environments. Thus, it is not necessary for the enduser to stock multiple different seal types for employment in various,specific operating conditions. This reduces overall cost to the end userbecause they need only purchase and stock a single seal type, the splitmechanical seal of the present invention, which can be adjusted toprovide a fluid seal under multiple operating conditions.

Those of ordinary skill will readily recognize that the illustratedsplit mechanical seal 10 of the present invention need not include therotary seal ring axial bore 183 in order for the seal to operate in itsintended manner. For example, in applications in which the possibilityof a negative pressure condition is unlikely, the rotary seal ring 16can be configured without the axial bore 183 without effecting theoperation and efficiency of the split mechanical seal 10.

As shown in FIGS. 6 and 11 the stationary seal ring 14 includes a pairof arcuate seal ring segments 200a, 200b each identical to the other.The stationary seal ring arcuate segments 200a, 200b have asubstantially smooth arcuate inner surface 202 extending parallel to thefirst axis 13 and an outer surface 204. The stationary seal ring segmentincludes seal face 18 and a first outer surface 206 that extends axiallytherefrom, as well as a further axially extending second outer surface208 that is stepped radially inward from the first outer surface 206.The first outer surface 206 and the second outer surface 208 form incombination therewith a first annular connecting wall 210 that extendsradially between the first and second outer surfaces. An axial extendingthird outer surface 212 is stepped radially inwardly from the secondouter surface 208 by a second annular connecting wall 214 that extendsradially between the second and third outer surfaces. The stationaryseal ring 14 has a substantially smooth arcuate bottom surface 216opposed to seal face 18. The stationary seal rings segments 200a, 200bhave a recess 220 formed along the bottom surface 216. The mechanicalspring clip 174. mechanically coupled to a bottom surface 55 of thegland assembly 30, seats in the recess 220 (FIG. 3 and 16). Thisarrangement helps align and seat the stationary seal ring 14 in thechamber 102, as well as provide a mechanical impedance for preventingthe stationary seal ring segment 14 from rotating with shaft 12 and therotary seal ring 16. A suitable mechanical clip is Chesterton MechanicalSeal Product No. 442, for sale by the A. W. Chesterton Co.

The inside diameter of the stationary segment inner surface 202 isgreater than the shaft 12 diameter, and is greater than the diameter ofthe inner surface 152 of the rotary seal ring 16, thereby allowingmotion of both the shaft 12 and the rotary seal 16 relative to thestationary seal ring 14. A plurality of elastomeric members, i.e. splitO-rings 222, 224, and 226, provides a radially inward biasing forcesufficient to place the segment sealing surfaces 22 of the stationaryseal ring segment 14 in sealing contact with the other stationary sealring segment. Additionally, the O-rings 222, 224, and 226 formfluid-tight and pressure-tight seals between the gland assembly 30 andthe stationary seal ring 14. The O-rings 222, 224 seat in the channels48, 46 formed in the third surface 42 of the gland assembly 30. TheO-ring 226 seats against the second surface 38 and the first annularconnecting wall 40 of the gland assembly 30. The stationary seal ring ispreferably composed of a carbon or ceramic material.

With reference to FIGS. 6, 11, and 15, a plurality of barrier fluidbores 228 are formed in the stationary seal ring segments 200a and 200b.The bores 228 include a radially extending section 230 that extendsradially inwardly from the second outer surface 208 of the stationaryseal ring segments and an axial section 232 that communicates with andextends from the radial section 230 to the seal face 18 of the seal ringsegments. Barrier fluid from a barrier fluid reservoir, not shown, isintroduced to the seal surfaces 18, 20 of the seal rings and the groove180 formed in the seal face 20 through the bores 228.

One skilled in the art will recognize that the barrier fluid bores arenot limited to the number or shape described and illustrated herein. Forexample, a single barrier fluid bore can be provided. Alternatively, itis possible to provide barrier fluid to the seal faces 18, 20 by meansother than a bore formed in the seal rings 14 and 16. For example, thebarrier fluid can be introduced to the seal faces from the outer and/orinner diameter of the seal ring segments through spiral pumping groovesor the like. In this manner, the barrier fluid does not necessarily needto be a separate fluid supply but can be the process medium itself.

Likewise, the position and arrangement of the barrier fluid bores is notlimited to those specifically disclosed herein, as alternative positionsand arrangements are possible to achieve the same results. For example,the barrier fluid bores can be formed in rotary seal ring 16, as well athe stationary seal ring 14, and can extend from the seal faces to anyouter surface of the seal rings. In addition, the barrier fluid bore canextend linearly from the seal faces 18, 20 to an outer surface of theseal ring.

An alternative arrangement of barrier fluid bores is shown in FIG. 6A.In addition to the barrier fluid bores 228, axial fluid bores 229 extendfrom the seal face 18 to the rear of the stationary seal ring 14, i.e.,second annular connecting wall 214. The fluid bores 228 and the axialfluid bores 229 are alternately arranged. in one practice, about thecircumference of the stationary seal ring 14. Although thisconfiguration of barrier fluid bores is operable with a barrier gas orliquid, it is particularly suited for applications in which a barrierliquid is introduced to the seal faces 18 and 20. The axial fluid bores229 transmit the barrier liquid from the seal face 18 to the secondannular connecting wall 214 at the rear of the stationary seal ring 14.In this manner, the fluid pressure at the rear of the stationary sealring is maintained at the fluid pressure at the seal face 18.Accordingly, this particular configuration permits the seal 10 to revertto a conventional balancing arrangement, and, thus operate as aconventional contacting face seal.

As best shown in FIG. 15, each radial section 230 of the barrier fluidbores 228 opens at the second outer surface 208 of the stationary sealring to provide fluid communication between the bores 228 and a similaraxial barrier fluid bore 234 formed in the gland assembly 30.

The bore 234 formed in the gland assembly 30 opens at one end at theouter surface 236 of the gland assembly and at the other end at asection 42b of the third surface 42 of the gland assembly 30 (FIGS. 1and 2). The O-rings 222 and 224 are positioned in grooves 48 and 46 oneither side of section 42b and provide fluid-tight and pressure-tightseals between the stationary seal ring segments 220a, 200b and the glandassembly 30. In this manner, a fluid-tight, pressure-tight annularchamber is formed between the O-rings 222, 224, section 42b of the glandassembly 30, and the second outer surface 208 of the stationary sealring 14, to retain the barrier fluid within this channel as well as toconduct the fluid into the axial bore 228. Barrier fluid from a barrierfluid reservoir (not shown) is supplied through the gland bore 234 andthe annular chamber to each of the stationary seal ring segment bores228.

The mechanical spring clip 174, in combination with O-ring 172.functions to provide an axial force for resilient supporting thestationary and rotary seal rings 14 and 16 to bias the seal rings suchthat the stationary and rotating seal surfaces 18 and 20 are biasedtowards each other. As illustrated in FIGS. 1 and 15, the seal rings 14and 16 are floatingly and non-rigidly supported in spaced floatingrelation relative to the rigid walls and faces of the gland and holderassemblies 30, 100. This floating and non-rigid support and spacedrelationship permits small radial and axial floating movements of therotary seal segments 150a, 150b and the stationary seal ring segments200a, 200b with respect to each other, while still allowing the rotatingseal face 20 to follow and to be placed into a sealing relationship withstationary seal ring face 18. Thus, the rotary and stationary sealsegments 150a, b and 200a, b are self-aligning as a result of thisfloating action.

In addition to the mechanical biasing provided by clip springs 174, anadditional fluid biasing system is provided in the seal 10 of thepresent invention. With reference to FIGS. 1, 11 and 15, the fluidbiasing system includes a radially extending closing fluid bore 240 thatis formed radially through the gland assembly 30 for introducing aclosing fluid which is introduced to a rear surface, such as outersurface 204, of the stationary seal ring segments 200a, 200b to providea closing force on the stationary and rotary seal rings 14, 16. Theradially extending closing fluid bore 240 is disposed adjacent andparallel to the barrier fluid bore 234. The closing fluid bore 240 opensat one end at the outer surface 236 of the gland assembly and at theother end at onto section 42a of the third inner gland surface 42 andthe second annular connecting wall 44 of the gland assembly 30. Afluid-tight and pressure-tight annular closing fluid chamber 242 isformed between O-rings 224, 226, the outer surface 204 of the stationaryseal ring segments 200a and 200b and the inner surface of the glandassembly.

As best illustrated in FIG. 15, closing fluid at a regulated pressure isprovided from a closing fluid reservoir (not shown) to the closing fluidchamber 242 through closing fluid bore 240. The closing fluid can be aliquid, a gas, or a combination of both. The closing fluid exerts afluid closing force F_(fc) on the stationary and rotary seal ringssegments. The fluid closing force F_(fc) operates in combination with amechanical spring closing force F_(sc) to bias the seal faces 18 and 20towards one another into a sealing relationship. Preferably, the sum ofthe fluid closing force F_(fc) and the mechanical spring closing forceF_(sc) balances the barrier fluid separation force F_(A) to inhibit overseparation of the seal faces 18 and 20 and the potential loss of theseal, e.g., excessive fluid leakage, between seal faces 18 and 20.

The magnitude of the fluid closing force F_(fc) can be adjusted orregulated by controlling the pressure of the closing fluid within theclosing fluid chamber 242. The ability to adjust the closing force onthe stationary and rotary seal rings segments provides significantadvantages. For instance, the magnitude of the closing force can bevaried to maintain a sealing relationship between the seal faces 18 and20 in the event of a change in operating conditions. Also, the magnitudeof the fluid closing force can be adjusted to compensate for changes inmechanical spring force due to use of seal components having differenttolerances. Consequently, the split mechanical seal 10 in combinationwith a fluid feedback system can dynamically regulate the fluid sealand/or the gap formed between the seal faces 18, 20 to control theamount of leakage during operation.

A significant advantage of the fluid biasing system is that it providesa simple integrated structure, such as fluid conduits, for externallycontrolling the amount of separation of the seal faces and regulatingthe fluid seal formed between the seal faces. Accordingly, this systemcan operate in combination with the separation force provided by barrierfluid introduced to the seal faces 18, 20 or independent of pressurizedfluid contained within the seal 10, to adjust the degree of seal facecontact. Hence, the split mechanical seal 10 can regulate or adjust theseal face separation, as well as the fluid seal formed therebetween,over a wide range of operating conditions. This increases theflexibility of the seal and allows the seal to be used in multipleenvironments.

One skilled in the art will recognize that the seal is not limited tothe specific fluid closing system described herein and that alternativefluid closing system arrangements are possible. For example, a singlefluid reservoir can be used to supply both barrier fluid to the grooveand to supply closing fluid to the outer surface of the stationary sealring. Alternatively, the process medium can be used as the closingfluid. Furthermore, either the mechanical spring clips 174 or theclosing fluid system can be used as the sole source of axial biasingforce, eliminating the need for the other axial closing force.

The split mechanical seal 10 of the present invention can include apressure feedback system (not shown) that regulates either or both ofthe closing pressure and the pressure of the barrier fluid supplied tothe seal to maintain the desired conditions at the seal faces 18, 20 ofthe seal rings 14, 16. The pressure control system can include pressuresensors mounted within or at the seal to monitor changes in barrier andclosing fluid pressure during operation. The pressure sensors can becoupled to a controller or the like in a closed or open feedback systemfor adjusting the barrier and/or closing fluid pressure in response topressure variations due to changes in operating conditions. Examples ofpressure feedback systems are disclosed in U.S Pat. No. 2,834,619 andU.S. Pat. No. 3,034,797, both of which are incorporated herein byreference.

Alternatively, the pressure feedback system can employ one of the systemfluids, such as barrier, process or closing fluid, as a regulator fluidinput and regulate either the barrier fluid pressure or closing forcebased on this regulated input. In doing this, the pressure feedbacksystem can sense a change in pressure between selected fluid pressuresand corrects any imbalance. The pressure feedback system accomplishesthis correction by connecting the system to a high pressure fluid supplyto add fluid to the system to raise the pressure therein or to ventpressure from the system when internal pressure is above a selectedvalue.

Barrier fluid can be introduced to outer surface 204 of the stationaryseal ring 14 through barrier fluid gland bore 234, as illustrated inFIGS. 1, 11, and 15. The O-rings 222 and 224, the outer surface 204 ofthe stationary ring segments, and the inner surface of the glandassembly form, in combination, a fluid-tight, pressure-tight chamber270. Barrier fluid introduced to the chamber 270 through gland bore 234exerts a radially inward fluid source F_(rb) on the outer surface 204 ofthe stationary seal ring segments. The radially inward fluid forceF_(rb) acts in combination with the radial inward force provided by theO-rings 222, 224, and 226 and the process medium, as well as a radiallyinward fluid force F_(rc) provided by the closing fluid within closingfluid chamber 242, to place each of the stationary seal ring segmentsealing surfaces 22 into sealing contact with another segment, therebymaintaining a fluid-tight, pressure-tight seal.

In a manner analogous to the rotary seal ring, the radially inward fluidforce F_(rb) can be adjusted or varied by controlling and/or regulatingthe pressure of the barrier fluid in the chamber 270. Likewise, theradially inward fluid force F_(rc) can be adjusted or varied bycontrolling and/or regulating the pressure of the closing fluid withinthe closing fluid chamber 242. In this manner, the radially inward forceon the stationary seal ring segments, in addition to the rotary sealring segments, can be adjusted for changes in operating conditions. Forexample, the radially inward force on the stationary seal ring segmentscan be increased to inhibit separation of the stationary seal ringsegments during negative pressure conditions.

As generally illustrated in FIG. 14. identical ball and socket fasteningmechanisms are provided on the free ends of O-rings 128, 170, 172, 222,224, and 226. At one end, the O-ring narrows into a substantiallyhemispherical shoulder portion 250 and, adjacent thereto, annular neckportion 252. Immediately adjacent neck portion 252 is substantiallyspherical head portion 254. In fastening, head portion 254 is insertedinto matching spherical socket portion 256 at the other end of theO-ring such that annular collar portion 258 surrounds and captures neckportion 252, and shoulder portion 250 is in intimate contact withannular jacket portion 260. Additionally, although seal 10 and itsassociated components are depicted as sectional pans, the O-rings 128,170, 172, 222, 224, and 226 are continuous and complete structureshaving the above configuration.

In assembly, the rotary seal segments 150a and 150b are mounted aboutthe shaft 12 and mounted in the holder assembly 100 by aligning thealignment bore 134 of the rotary seal ring with axially extendingalignment pin 132, which extends from alignment bore 130 of the holderassembly. The O-ring 170 is concentrically disposed about the rotaryseal segments 150a and 150b and is further placed in sealing contactwith the holder second face 112, rotary seal second outer surface 158,and can contact either holder first wall 118 or rotary seal first wall160. Likewise, the O-ring 172 is concentrically disposed about therotary seal segments 150a and 150b and is further placed in sealingcontact with the holder fourth face 115, the holder third wall 121,rotary seal fourth outer surface 166, and rotary seal third wall 168.The O-rings 170 and 172 provide an inward radial force sufficient toplace the rotary seal surfaces 24 of the seal segment 150a into sealingcontact with each of the seal surfaces 24 of the seal segment 150b. Theholder segments 34a and 34b are then secured together by tighteningscrews 146 that are positively maintained in fastener receivingapertures 144. As shown in FIGS. 1 and 15, the rotary seal segments 150aand 150b are spaced from the holder assembly inner surface 108, and arenon-rigidly supported therein by O-rings 170 and 172, thereby permittingsmall radial and axial floating movements of the rotary seal ring 16.

The stationary seal ring segments 200a and 200b are concentricallymounted over shaft 12 and secured together by O-rings 222, 224, and 226.The O-rings 222, 224, and 226 provide a radially inward force to thestationary seal ring outer surface 204 sufficient to place the sealingsurfaces 22 of the seal segment 200a into sealing contact with thesealing surfaces 22 of the seal segment 200b.

The gland segments 34a and 34b are concentrically placed about theholder assembly 100, and the stationary and rotary seal rings 14 and 16,and are secured together by screws 90 that are mounted in and positivelymaintained by fastener-receiving apertures 84 in the gland segments. Thescrew cannot be unintentionally removed from the seal 10 since they aresecured to the gland assembly 30 by the inventive fastener-receivingaperture 84 and screw 90. Additionally, mounting the screws 90 does notnecessitate rotating the shaft since the screws 90 can be reached fromeither side of the gland assembly 30. Alternative seal fastening meansknown in the art can also be used with the seal of the presentinvention.

Prior to fully securing the gland assembly 30 to the housing 11. theshaft 15 12, the holder assembly 100, and the stationary and rotary sealrings 14, 16 should be centered within the chamber 102. Examples ofsuitable centering mechanisms are described in U.S. Pat. No. 5,571,268,which is assigned to the assignee hereof and is incorporated herein byreference.

When the gland assembly 30 and the holder assembly 100 are properlyaligned, the gland gasket 80 and the holder gasket 142 are captured inseparate gasket grooves 64, 140 formed on opposing seal faces of thegland and holder segments. The double capture configuration allows theseal 10 to withstand higher pressures without degradation of thepressure and fluid seals formed at the segment sealing faces.Additionally, the O-rings 222, 224, and 226 form a pressure-tight andfluid-tight seal between the gland inner surface and the outer surface204 of the stationary seal ring 14.

After the seal 10 is assembled and mounted to the pump housing 11, theprocess medium is sealed within a process fluid chamber 300, as shown inFIGS. 1 and 15. The process fluid chamber is defined by the gland innerfourth surface 50 and fifth surface 54, the gland third wall 52, O-rings170 and 222, the outer surface 106 and the first and second innersurfaces 110, 112 of the holder assembly, first outer surface 156 of therotary seal ring 16, and the first and second outer surfaces 206, 208and first connecting wall 210 of the stationary seal ring 14. Theambient medium, typically air, fills an ambient fluid chamber 310,typically sealed from the process chamber 300, that is defined by thestationary and rotary seal ring inner surfaces 152, 202, the fourth wall169 of the rotary seal ring 16, the O-ring 128, and the shaft 12. Theterms "ambient" and "ambient medium" are intended to include anyexternal environment or medium other than the process environment orprocess medium.

The stationary and rotating segment seal surfaces 22, 24 are placed insealing contact with the other segment of the pair by the radial forceof the O-rings 170, 172, 222, 224, and 226. The pressure of the processmedium within the process chamber 300 exerts an additional radial inwardforce, proportional to the process fluid pressure, upon the rotary sealring segment first outer surface 156 and the stationary seal ringsegment first and second outer surfaces 206, 208, biasing the segmentsealing surfaces 22, 24 together.

The O-ring 128 prevents the seepage of process fluid along the shaft 12and into the ambient fluid chamber 310. The flat gasket 60 prevents theseepage of process fluid along the housing 11 and the seal 10 interface.The O-rings 170, 172, 222, 224, and 226 prevent process fluid frominvading the ambient fluid chamber 310 by way of the holder assembly 100and the gland assembly 30, respectively.

In operation, barrier fluid is introduced to the groove 180 and the sealfaces 18, 20a, 20b through barrier fluid bores 228 in the stationaryseal ring 14. The barrier fluid exerts a primarily hydrostatic liftingforce on the seal face 18, 20a, and 20b that operates to separate atleast a portion of the stationary seal ring face 18 from at least aportion of the rotary seal ring faces 20a and 20b to form a gaptherebetween. The barrier fluid fills the gap formed between the sealfaces, thereby separating the seal faces 18 and 20 to form a fluid sealbetween the process medium in the process chamber 300 and the ambientfluid in the ambient fluid chamber 310. The gap is maintained at apredetermined width, or is adjustable, to minimize leakage across theseal faces while concomitantly separating the seal faces to reduce wear.

The effects of the barrier fluid on the seal 10 is twofold. First, thebarrier fluid can reduce wear on the seal faces by reducing the amountof direct, frictional contact between the seal face 18 and the sealfaces 20a and 20b, thus resulting in a longer life for the sealcomponents. Second, the barrier fluid operates to transfer heatgenerated by the direct, frictional contact between the seal faces awayfrom the seal faces, resulting in a more even temperature distributionthroughout the seal 10 and thus prolonging the useful life of the sealcomponents by reducing thermal stress that the components are subjectedto.

Additionally, the split mechanical seal 10 of the present inventionprovides the requisite flexibility of being operable with differenttypes of barrier fluids, e.g. gases or liquids or combinations thereof.This flexibility is possible because the area of direct, frictionalcontact between the seal faces can be controlled by adjusting thebarrier fluid pressure and the closing fluid pressure, and thus themagnitude of the hydrostatic lifting force, to produce the desiredseparation gap. Generally. it is desirable for the separation gap to begreater in barrier gas applications than in barrier liquid applications,because of the typically better heat transfer properties of liquidscompared with gases. Accordingly, in applications in which a barrier gasis preferred, the separation gap can be adjusted to the appropriatewidth for the selected barrier gas which will inhibit wear on the sealfaces. Similarly, in applications in which a barrier liquid ispreferred, the separation gap can be adjusted to the appropriate widthfor the selected barrier liquid which will inhibit wear on the sealfaces.

The seal 10 of the present invention offers the further advantage ofbeing a completely split mechanical seal, and preferably a splitmechanical non-contacting face seal, in which a portion of each of theseal components, e.g. the gland assembly, the holder assembly, thestationary and rotary seal rings, and the O-rings, is split. This splitseal design facilitates replacement or repair of damaged seal componentsby permitting installation and removal of the split seal componentswithout necessitating the complete breakdown of the associatedequipment, e.g., a pump or the like, and without having to pass the sealover the end of the shaft.

Furthermore, the split configuration of the split mechanical seal 10 ofthe present invention does not compromise the seal integrity of theseal. The inventive design of the seal 10 is such that radial fluidleakage at the seal surfaces 22, 24, 62, and 138, between each of thesplit segments 150, 200, 34, and 104 of the stationary and rotary sealrings, the gland assembly, and the holder assembly, respectively, isinhibited. Similarly, fluid leakage across the stationary and rotaryseal faces 18, 20a and 20b is inhibited by the combination of axialclosing forces applied to the seal rings which function to bias the sealfaces towards each another in a sealing relationship, as well asmaintain the proper alignment of the seal faces.

During normal operation, the pressure of the process medium in theprocess fluid chamber 300 is greater than the pressure of the ambientfluid in the ambient fluid chamber 310 (the positive pressurecondition), and the process fluid exerts a radially inward force on theouter surfaces 204, 154 of the stationary and rotary seal rings,respectively, and the outer surface 106 of the holder assembly 100, asillustrated in FIGS. 1 and 15. The radially inward force exerted by theprocess medium assists in holding together the segments of the sealrings and the holder assembly in a fluid sealed relationship.

If the pressure of the process medium in the process fluid chamber 300falls below the pressure of the ambient fluid in the ambient fluidchamber 310 (the negative pressure condition), the ambient fluid exertsa radially outward force on the inner surfaces 202, 152 of thestationary and rotary seal rings, respectively. If the pressuredifferential created during this condition is such that the radiallyoutward force is greater the radially inward force applied by theO-rings, the seal ring segments can separate, resulting in leakageacross the seal faces.

To prevent this type of leak-age across the seal faces 18, 20, and sealsurfaces 22, 24 in the negative pressure condition, the radially outwardforce on the seal rings from the ambient fluid pressure is counterbalanced by the radial inward force provided by the O-rings 222, 224,and 226 on the stationary seal ring segments 200a and 200b and byO-rings 170 and 172 on the rotary seal ring segments 150a and 150b, incombination with the radially inward force exerted by the barrier fluiddisposed within the chamber 185 on the outer surface 154 of the rotaryseal ring segments. The radially inward fluid force F_(rr) acts incombination with the radial inward force provided by O-rings 170 and 172to maintain each of the rotary segment sealing surfaces 24 into sealingcontact with the other segment during this condition, therebymaintaining a fluid-tight and pressure-tight seal.

During operation, the O-ring 172 acts a pivoting resilient member aboutwhich the rotary seal ring 16 can pivot to maintain co-planar alignmentand a sealing relationship between the rotary seal ring seal face 18 andthe stationary seal ring seal face 20. Thus, coning of the seal faces isprevented and loss of the fluid seal between the seal faces inhibited.Additionally, the presence of the O-ring 172 and the pivoting ability itaffords allows for the seal faces 20a and 20b to be radially separatedto form concentric seal faces without loss of the fluid seal betweenseal faces 18 and 2a, b. Accordingly, the pivoting action of the O-ring172 provides for a resilient pivoting of the rotary seal ring 16 duringfull operation of the split mechanical seal 10 in both non-contactingand contacting face seal modes, while concomitantly ensuring eitherconsistent co-planar contact between the opposed seal faces.

The fluid biasing system introduces a closing fluid to the outer surface204 of the stationary seal ring segments 200a, 200b to provide a closingforce on the stationary and rotary seal rings 14, 16. Closing fluid at aregulated pressure is provided to the closing fluid chamber 242 throughclosing fluid bore 240. The closing fluid exerts a fluid closing forceF_(fc) on the stationary and rotary seal rings segments. The fluidclosing force F_(fc) operates in combination with a mechanical springclosing force F_(sc) to bias the seal faces 18 and 20 towards oneanother into a sealing relationship. During operation, the sum of thefluid closing force F_(fc) and the mechanical spring closing forceF_(sc) balances the barrier fluid separation force F_(A) to inhibit overseparation of the seal faces 18 and 20 and the potential loss of theseal, e.g., excessive fluid leakage, between seal faces 18 and 20.

The fluid biasing system increases the flexibility of the splitmechanical seal 10 and allows the seal to be used in multipleenvironments by providing a simple integrated structure, i.e., fluidconduits, for externally controlling the amount of separation of theseal faces and regulating the fluid seal formed between the seal faces.The system can operate in combination vvith the separation forceprovided by barrier fluid on the seal faces 18, 20 or independent ofpressurized fluid contained within the seal 10 to adjust the degree ofseal face contact. Thus, the split mechanical seal 10 can regulate oradjust the seal face separation, as well as the fluid seal formedtherebetween, over a wide range of operating conditions.

One skilled in the art will recognize that, although only a single sealconfiguration is described and illustrated herein, the seal 10 of thepresent invention can be used in a dual or tandem or plural sealconfiguration in which multiple seals 10 or seal rings are arrangedaxially along the shaft.

It will thus be seen that the invention efficiently attains the objectsset forth above, among those made apparent from the precedingdescription. Since certain changes may be made in the aboveconstructions without departing from the scope of the invention, it isintended that all matter contained in the above description or shown inthe accompanying drawings be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are to cover allgeneric and specific features of the invention described herein, and allstatements of the scope of the invention which, as a matter of language,might be said to fall therebetween.

Having described the invention, what is claimed as new and desired to besecured by Letters Patent is:
 1. A split mechanical non-contacting faceseal for providing fluid sealing between a housing and a rotating shaft,said seal comprisinga first seal ring having at least two split sealring segments and a radially extending first seal face, a second sealring having at least two split seal ring segments and a radiallyextending second seal face, said first and second seal faces beingopposed to one another, one of said first seal ring and said second sealring being connected to said rotating shaft to rotate therewith, theother of said first seal ring and said second seal ring being connectedto said housing, means for introducing a fluid to said first seal faceand said second seal face, and a resilient member positioned about saidsecond seal ring to permit pivoting of said second seal ring about saidresilient member to maintain said first and second seal faces inco-planar alignment.
 2. The split mechanical seal according to claim 1,further comprising a split gland assembly having at least two glandsegments coupled to an outer surface of said first seal ring forconnecting said first seal ring to said housing.
 3. The split mechanicalseal according to claim 2, further comprising at least one splitresilient member interposed between said split gland assembly and saidouter surface of said first seal ring for resiliently engaging saidfirst seal ring to form a seal therebetween.
 4. The split mechanicalseal according to claim 1, further comprising a split holder assemblyhaving at least two holder segments coupled to an outer surface of saidsecond seal ring for coupling said second seal ring to said rotatingshaft.
 5. The split mechanical seal according to claim 4 furthercomprising at least one split resilient member interposed between saidsplit holder assembly and said outer surface of said second seal ringfor resiliently engaging said second seal ring to form a sealtherebetween.
 6. The split mechanical seal according to claim 1, furthercomprisinga split gland assembly having at least two gland segmentscoupled to an outer surface of said first seal ring for connecting saidfirst seal ring to said housing, a second resilient member interposedbetween said split gland assembly and said outer surface of said firstseal ring for resiliently engaging said first seal ring to inhibitradial separation of said seal ring segments of said first seal ring andto form a seal therebetween, and a split holder assembly having at leasttwo holder segments coupled to an outer surface of said second seal ringfor coupling said second seal ring to said rotating shaft, wherein saidresilient member is interposed between said split holder assembly andsaid outer surface of said second seal ring for resiliently engagingsaid second seal ring to inhibit radial separation of said seal ringsegments of said second seal ring and to form a seal therebetween. 7.The split mechanical seal according to claim 6, further comprising athird resilient member interposed between said split holder assembly andsaid outer surface of said second seal ring for resiliently engagingsaid second seal ring to inhibit radial separation of said seal ringsegments of said second seal ring and to form a seal therebetween. 8.The split mechanical seal according to claim 7, wherein said thirdresilient member selectively abuts one of said outer surface of saidsecond seal ring and an inner surface of said holder assembly.
 9. Thesplit mechanical seal according to claim 1, further comprising fluidintroduction means for introducing a closing fluid to a rear surface ofsaid first seal ring to provide a closing force on said first seal ring,said closing force biasing said first and second sealing faces towardsone another.
 10. The split mechanical seal according to claim 1, whereinsaid means for introducing a fluid comprises a groove formed in saidsecond seal face.
 11. The split mechanical seal according to claim 10,wherein said groove is continuous about said second seal face.
 12. Thesplit mechanical seal according to claim 10, wherein said groove ispositioned on said second seal face to form two concentric seal facesthereby providing a dual seal on a single seal ring.
 13. The splitmechanical seal according to claim 10, further comprising means forproviding a separation force between said first and second seal faces tocause separation of said at least a portion of said first seal face fromat least a portion of said second seal face.
 14. The split mechanicalseal according to claim 13, wherein said separation force comprisesgenerally primarily a hydrostatic separation force.
 15. The splitmechanical seal according to claim 1, wherein said means for introducinga fluid to said first and second seal faces comprises a fluid conduitformed through said first seal ring.
 16. The split mechanical sealaccording to claim 15, wherein said fluid conduit extends axiallythrough said first seal ring and has a first end opening onto said firstseal face.
 17. The split mechanical seal according to claim 1, whereinsaid means for introducing a fluid to said first and second seal facescomprisesa continuous, circumferential groove formed in said first sealface, and a fluid conduit formed through said second seal ring, saidfluid conduit opening onto said second seal face and onto said groovewhen said seal rings are assembled to provide fluid communicationbetween said fluid conduit and said groove.
 18. The split mechanicalseal according to claim 1, further comprising means for fluidlyretaining together said seal ring segments of said second seal ring in asealing relationship in a negative pressure condition.
 19. The splitmechanical seal according to claim 18, wherein said means for fluidlyretaining said seal ring segments of said second seal ring in a sealingrelationship comprises a fluid conduit formed in said second seal ringfor supplying fluid to an outer surface of said second seal ring. 20.The split mechanical seal according to claim 19, wherein said fluidconduit has first and second ends, said first end opening onto saidsecond seal face and being disposed in fluid communication with saidmeans for introducing fluid to said first and second seal faces, andwherein said second end of said fluid conduit opens at said outersurface of said second seal ring.
 21. The mechanical seal according toclaim 1, wherein said means for introducing a fluid to said first andsecond seal faces establishes a gap having a selected width between saidfirst and second seal surfaces, said seal further comprising adjustmentmeans for adjusting the gap width during operation.
 22. The mechanicalseal according to claim 21, wherein said adjustment means comprisesfluid introduction means for introducing a closing fluid to a rearsurface of said first seal ring to provide a selectively variableclosing force on said first seal ring for adjusting the gap width duringoperation.
 23. A split mechanical non-contacting face seal for providingfluid sealing between a housing and a rotating shaft, said sealcomprisinga stationary seal ring having at least two seal ring segmentsand a radially extending first seal face, a rotary seal ring having atleast two seal ring segments and a radially extending second seal face,said first and second seal faces being opposed to one another, means forintroducing a barrier fluid to said first seal face and said second sealface for separating at least a portion of said first seal face from atleast a portion of aid second seal face, a split gland assembly havingat least two gland segments coupled to an outer surface of saidstationary seal ring for connecting said stationary seal ring to saidhousing, a first split resilient member interposed between said splitgland assembly and said outer surface of said stationary seal ring forresiliently engaging said stationary seal ring to form a sealtherebetween, a split holder assembly having at least two holdersegments coupled to an outer surface of said rotary seal ring forcoupling said rotary seal ring to said rotating shaft, and a secondsplit resilient member interposed between said split holder assembly andsaid outer surface of said rotary seal ring for resiliently engagingsaid rotary seal ring to form a seal therebetween, said second resilientmember being positioned to permit pivoting of said rotary seal ringabout said second split resilient member to maintain alignment of saidfirst seal face with said second seal face.
 24. The split mechanicalseal according to claim 23, further comprising means for introducing aclosing fluid to a rear surface of said stationary seal ring to providea closing force on said stationary seal ring, said closing force biasingsaid first and second sealing faces towards one another.
 25. The splitmechanical seal according to claim 23, wherein said split gland assemblyfurther comprises a barrier fluid conduit formed therein, said barrierfluid conduit being positioned proximate and in fluid communication withsaid means for introducing a barrier fluid to said first and second sealfaces.
 26. The split mechanical seal according to claim 23, wherein saidmeans for introducing a fluid to said first and second seal facescomprisesa continuous, circumferential groove formed in said second sealface, and a fluid conduit formed through said stationary seal ring, saidfluid conduit opening onto said first seal face and onto said groovewhen said seal rings are assembled to provide fluid communicationbetween said fluid conduit and said groove.
 27. The split mechanicalseal according to claim 23, further comprising means for fluidlyretaining together said seal ring segments of said rotary seal ring in asealing relationship in a negative pressure condition.
 28. The splitmechanical seal according to claim 23, further comprising a third splitresilient member interposed between said split holder assembly and saidouter surface of said rotary seal ring for resiliently engaging saidrotary seal ring to inhibit radial separation of said seal ring segmentsof said rotary seal ring and to form a seal therebetween.
 29. The splitmechanical seal according to claim 28, wherein said third splitresilient member selectively abuts one of said outer surface of saidrotary seal ring and an inner surface of said holder assembly.
 30. Themechanical seal according to claim 23, wherein said means forintroducing a fluid to said first and second seal faces establishes agap having a selected width between said first and second seal surfaces,said seal further comprising adjustment means for adjusting the gapwidth during operation.
 31. The mechanical seal according to claim 30,wherein said adjustment means comprises fluid introduction means forintroducing a closing fluid to a rear surface of said stationary sealring to provide a selectively variable closing force on said stationaryseal ring for adjusting the gap width during operation.
 32. A splitmechanical face seal for providing fluid sealing between a housing and arotating shaft, said seal comprisinga first seal ring having at leasttwo split seal ring segments and a radially extending first seal face, asecond seal ring having at least two split seal ring segments and aradially extending second seal face, said first and second seal facesbeing opposed to one another, one of said first seal ring and saidsecond seal ring being connected to said rotating shaft to rotatetherewith, the other of said first seal ring and said second seal ringbeing connected to said housing, means for introducing a fluid to saidfirst seal face and said second seal face, and a resilient memberpositioned about said second seal ring to permit pivoting of said secondseal ring about said resilient member to maintain said first and secondseal faces in co-planar alignment.
 33. The split mechanical sealaccording to claim 32, further comprising a split gland assembly havingat least two gland segments coupled to an outer surface of said firstseal ring for connecting said first seal ring to said housing.
 34. Thesplit mechanical seal according to claim 33, further comprising at leastone split resilient member interposed between said split gland assemblyand said outer surface of said first seal ring for resiliently engagingsaid first seal ring to form a seal therebetween.
 35. The splitmechanical seal according to claim 32, further comprising a split holderassembly having at least two holder segments coupled to an outer surfaceof said second seal ring for coupling said second seal ring to saidrotating shaft.
 36. The split mechanical seal according to claim 35,further comprising at least one split resilient member interposedbetween said split holder assembly and said outer surface of said secondseal ring for resiliently engaging said second seal ring to form a sealtherebetween.
 37. The split mechanical seal according to claim 32,further comprisinga split gland assembly having at least two glandsegments coupled to an outer surface of said first seal ring forconnecting said first seal ring to said housing, a second resilientmember interposed between said split gland assembly and said outersurface of said first seal ring for resiliently engaging said first sealring to inhibit radial separation of said seal ring segments of saidfirst seal ring and to form a seal therebetween, and a split holderassembly having at least two holder segments coupled to an outer surfaceof said second seal ring for coupling said second seal ring to saidrotating shaft, wherein said resilient member is interposed between saidsplit holder assembly and said outer surface of said second seal ringfor resiliently engaging said second seal ring to inhibit radialseparation of said seal ring segments of said second seal ring and toform a seal therebetween.
 38. The split mechanical seal according toclaim 37, further comprising a third resilient member interposed betweensaid split holder assembly and said outer surface of said second sealring for resiliently engaging said second seal ring to inhibit radialseparation of said seal ring segments of said second seal ring and toform a seal therebetween.
 39. The split mechanical seal according toclaim 38, wherein said third resilient member selectively abuts one ofsaid outer surface of said second seal ring and an inner surface of saidholder assembly.
 40. The split mechanical seal according to claim 32,further comprising fluid introduction means for introducing a closingfluid to a rear surface of said first seal ring to provide a closingforce on said first seal ring, said closing force biasing said first andsecond sealing faces towards one another.
 41. The split mechanical sealaccording to claims 32, wherein said means for introducing a fluidcomprises a groove formed in said second seal face.
 42. The splitmechanical seal according to claim 41, wherein said groove is continuousabout said second seal face.
 43. The split mechanical seal according toclaim 41, wherein said groove is positioned on said seal surface to formtwo concentric seal faces thereby providing a dual seal on a single sealring.
 44. The split mechanical seal according to claim 41, furthercomprising means for providing a separation force between said first andsecond seal faces to cause separation of said at least a portion of saidfirst seal face from at least a portion of said second seal face. 45.The split mechanical seal according to claim 44, wherein said separationforce comprises generally primarily a hydrostatic separation force. 46.The split mechanical seal according to claim 32, wherein said means forintroducing a fluid to said first and second seal faces comprises afluid conduit formed through said first seal ring.
 47. The splitmechanical seal according to claim 32, wherein said means forintroducing a fluid to said first and second seal faces comprisesacontinuous, circumferential groove formed in said first seal face, and afluid conduit formed through said second seal ring, said fluid conduitopening onto said second seal face and onto said groove when said sealrings are assembled to provide fluid communication between said fluidconduit and said groove.
 48. The split mechanical seal according toclaim 32, further comprising means for fluidly retaining together saidseal ring segments of said second seal ring in a sealing relationship ina negative pressure condition.
 49. The split mechanical seal accordingto claim 32, wherein said means for fluidly retaining together said sealring segments comprises a fluid conduit formed in said second seal ringfor supplying fluid to an outer surface of said second seal ring. 50.The split mechanical seal according to claim 49, wherein said fluidconduit has first and second ends, said first end opening onto saidsecond seal face and being disposed in fluid communication with saidmeans for introducing fluid to said first and second seal faces, andwherein said second end of said fluid conduit opens at said outersurface of said second seal ring.
 51. The mechanical seal according toclaim 32, wherein said means for introducing a fluid to said first andsecond seal faces establishes a gap having a selected width between saidfirst and second seal surfaces, said seal further comprising adjustmentmeans for adjusting the gap width during operation.
 52. The mechanicalseal according to claim 51, wherein said adjustment means comprisesfluid introduction means for introducing a closing fluid to a rearsurface of said first seal ring to provide a selectively variableclosing force on said first seal ring for adjusting the gap width duringoperation.